1. Field of the Invention
The invention relates in general to electrical insulating bushings, and more specifically to electrical insulating bushings capable of operating satisfactorily at elevated temperatures.
2. Description of the Prior Art
Conventional insulating bushings for electrical apparatus, such as transformers, circuit breakers, and the like, normally have an ambient temperature limitation of about 100.degree. C. Hot precipitators used to remove solid particles in hot exhaust gases operate in an ambient above 150.degree. C, and it would be desirable to mount the power supply for such precipitators on the precipitator itself in order to reduce the distance between the high voltage bushing of the power supply and the plates of the precipitator.
Attempts to use a conventional electrical bushing in the precipitator power supply have resulted in early bushing failure due to one or more causes, such as thermal run away of the porcelain insulating member, dielectric failure of the insulating papers and mineral oil, and thermally induced leaks in the bushing assembly which enable the insulating fluid to escape from the bushing cavity. Baffling may be installed in the duct work between the power supply and the precipitator to protect the electrical bushing from direct contact with the hot gases, but the baffling adds substantially to the cost and maintenance of a precipitator installation. Thus, it would be desirable to provide a new and improved bushing assembly which will withstand operation in an ambient of 150.degree. C, enabling such apparatus as power supplies for hot precipitators to be mounted directly on the precipitator without requiring auxiliary baffling, and without premature bushing failure.